Importance of Rubisco activase in maize productivity based on mass selection procedure

Abstract

The original maize (Zea mays L.) var. Zacatecas 58 (Z0) and five composites of cycles 5, 10, 15, 20, and 23 of stratified mass selection (Z5, Z10, Z15, Z20, and Z23) for improved productivity applied to the original variety were used as the model system. Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) (Rubisco) activity and the rates of net photosynthesis in the leaves above the ear were compared in all the composites during the grain filling period. Leaves were sampled weekly from anthesis to physiological maturity. Results showed a significant and gradual increase in Rubisco activity for the improved populations. In vivo photosynthesis measured by IRGA during the same period also showed increased levels associated with increases of grain yield. The highest Rubisco activity, photosynthetic rate and grain yield were found in the Z23 population. Western blot analysis for Rubisco protein did not show significant differences either during the filling period or between populations. The same analysis, however, for Rubisco activase protein showed increasing contents in the improved populations. These data confirm and complement previous findings, indicating that the stratified visual mass selection procedure applied to maize plants is associated with leaf content of Rubisco activase protein. The possible regulatory role of Rubisco activase during grain filling is discussed.